Process control system and a mold assembly for expandable plastic containers

Abstract

A mold assembly for forming a container made of expandable thermoplastic particles, e.g. expandable polystyrene particles, comprises an inner mold and an outer mold, which when assembled form a mold cavity for receiving the thermoplastic particles. Steam and cooling fluid are supplied to passageways in the inner mold and outer mold. Temperature sensing devices, e.g. thermocouples, permanently mounted to the inside wall of the inner mold and to the outside wall of the outer mold, detect the temperature of the mold assembly. Pressure transducers in communication with the steam and cooling fluid being supplied into the passageways detect the pressure of the steam and water supplied to the passageways. These devices are continuously operative throughout the supply of steam and cooling fluid in the molding cycle to adjust the pressure and/or cycle time of the steam and to adjust the cycle time of the cooling fluid to optimally fuse together and cool the particles in the mold assembly.

1 . A mold assembly for molding a container from expandable plastic particles in a molding cycle, the container having a bottom wall, and a sidewall extending upwardly from the bottom wall to a mouth of the container, the mold assembly comprising: 
 an inner mold and an outer mold assembled together to form a mold cavity defining the container;    port means in communication with the outer mold for delivering expandable plastic particles into the mold cavity,    passageway means for carrying steam and cooling fluid into the inner mold and the outer mold adjacent the mold cavity and extending adjacent that part of the mold cavity defining the bottom wall and sidewalls of the container;    conduit means for delivering steam and cooling fluid into said passageway means;    temperature sensing means mounted to an inner wall of said inner mold and to an outer wall of said outer mold for sensing the temperature of the mold assembly;    pressure transducer means in association with said conduit means for sensing the pressure of the steam and the cooling fluid in said conduit means; and    control means in communication with the temperature sensing means and the pressure transducer means for continuously monitoring the temperature of the mold assembly and the pressure of the steam in said conduit means and adjusting at least the pressure and/or cycle time of the steam to optimally fuse the expandable plastic particles, and for continuously monitoring the temperature of the mold assembly and the pressure of the cooling fluid in said conduit means and adjusting at least the cycle time of the cooling fluid to optimally cool the expandable plastic particles in the mold assembly during the molding cycle for the forming of a container.    
   
   
       2 . A mold assembly of  claim 1  wherein said temperature sensing means are permanently mounted to the inner mold and the outer mold of said mold assembly.  
   
   
       3 . A mold assembly of  claim 2  wherein said temperature sensing means is comprised of thermocouples permanently mounted to said inner mold and to said outer mold of said mold assembly.  
   
   
       4 . A mold assembly of  claim 1  further comprising juncture conduit means connected to said conduit means for delivering the steam and cooling fluid into said passageways in the mold assembly, and wherein said pressure transducer means is attached to and in communication with said juncture conduit means.  
   
   
       5 . A mold assembly of  claim 1  wherein said control means comprises integrated data acquisition means including means for adjusting the pressure and/or cycle time of the steam in the passageways in the mold assembly to optimally fuse and cool the expandable plastic beads.  
   
   
       6 . A process for continuously monitoring the pressure of the steam or cooling fluid delivered through conduit means into passageways of a mold assembly for forming a container made of expandable plastic particles, the steps comprising: 
 providing permanently mounted temperature sensing means on the mold assembly for sensing the temperature of the mold assembly,    providing pressure transducer means for sensing the pressure of the steam or cooling fluid and in communication with said conduit means that delivers the steam or cooling fluid into said passageways of the mold assembly, and    continuously monitoring the temperature of the mold assembly and the pressure of the steam and adjusting at least the pressure and/or cycle time of the steam in the molding assembly to optimally fuse the expandable plastic particles, and for continuously monitoring the temperature of the mold assembly and the pressure of the cooling fluid and adjusting at least the cycle time of the cooling fluid to optimally cool the expandable plastic particles in the mold assembly in the forming of the container.    
   
   
       7 . A process for optimally fusing expandable plastic beads in a mold assembly to form a container by using the process of  claim 6 .  
   
   
       8 . A process for optimally cooling expandable plastic beads in a mold assembly to form a container by using the process of  claim 6 .  
   
   
       9 . A control system for a mold assembly for molding a container from expandable plastic particles, the container having a bottom wall, and a sidewall extending upwardly from the bottom wall to a mouth of the container, the process control system comprising: 
 a mold assembly having an inner mold and an outer mold which are assembled to form a mold cavity defining the container;    port means in communication with the outer mold for delivering expandable plastic beads into the mold cavity,    passageway means for delivering steam and cooling fluid in at least one the inner mold or outer mold adjacent the mold cavity and extending adjacent that part of the cavity defining the sidewall and the bottom wall of the container;    conduit means for delivering steam and cooling fluid into said passageway means;    temperature sensing means permanently affixed to the inner mold and the outer mold for sensing the temperature of the mold assembly;    pressure transducer means in association with said conduit means for sensing the pressure of the steam and cooling fluid in the conduit means; and    control means in communication with said temperature sensing means and said pressure transducer means for continuously monitoring the temperature of the mold assembly and the pressure of the steam in the conduit means and adjusting at least the pressure and/or cycle time of the steam to optimally fuse the expandable plastic beads, and for continuously monitoring the temperature of the mold assembly and the pressure of the cooling fluid in the conduit means and adjusting at least the cycle time of the cooling fluid to optimally cool the expandable plastic particles in the mold assembly in the forming of said container.    
   
   
       10 . A control system of  claim 9  wherein said control means comprises integrated data acquisition means including means for adjusting the pressure and/or cycle time of the steam in the passageways in the mold assembly to optimally fuse and cool the expandable plastic beads.  
   
   
       11 . A control system of  claim 9  wherein said temperature sensing means are permanently mounted to the inner mold and outer mold of the mold assembly.  
   
   
       12 . A control system of  claim 9  wherein said temperature sensing means is comprised of thermocouples permanently mounted to said inner mold and to said outer mold of said mold assembly.  
   
   
       13 . A control system of  claim 9  further comprising juncture conduit means connected to said conduit means for delivering the steam and cooling fluid into said passageways in the mold assembly, and wherein said pressure transducer means is attached to and in communication with said juncture conduit means.